Relationship between occlusal force and endothelial function in community‐dwelling elderly women: A pilot study

Abstract Objective In this study, age, endothelial function as flow‐mediated dilation (FMD), occlusal force, grip strength, and advanced glycation end products (AGEs) were obtained. AGEs were measured as indicators of aging, while grip strength was measured as an indicator of muscle strength. This study aimed to explain the relationship between occlusal force and endothelial function and determine whether occlusal force can be a new indicator in community preventative care projects. Materials and Methods In 38 community‐dwelling women (age, 76.7 ± 5.7 years), the occlusal force and grip strength were measured, the endothelial function was evaluated by FMD, and AGEs were obtained. The relationship between occlusal force, measurement items, and factors were investigated independently related to endothelial function. Results There were significant correlations between occlusal force and grip strength (r = .54, p < .01). The degree of FMD was significantly associated with occlusal force (r = .60, p < .01) and grip strength (r = .35, p < .05) or increase in AGEs (r = −.37, p < .05). Multiple regression analysis revealed that occlusal force was significantly associated with the degree of FMD (p < .01). Conclusion Occlusal force can be an important indicator of endothelial function in the community‐dwelling elderly. This study may help understand the general health of the elderly in communities.


| INTRODUCTION
To have a long life in a community, it is important to prolong the healthy life expectancy and the duration of living without requiring any assistance for activities of daily living (ADLs). Accordingly, it is essential to maintain and improve the physical strength and quality of life (QOL) of the elderly through preventative care in a community.
Endothelial function is also related to lifestyle habits, (Wang & Widlansky, 2009) such as diet and exercise, (Rossman et al., 2017) and it is assessed by flow-mediated dilation (FMD). A decreased FMD increases the risk of arteriosclerosis, cerebrovascular disease, and myocardial infarction (Ras et al., 2013;Targonski et al., 2003). These diseases may have residual sequelae even after recovery and can be considered risk factors for shortening the healthy life expectancy. Both occlusal force and FMD can be important indicators of the general condition of the elderly and can be used for appropriate preventative care measures in communities. However, to measure FMD, a specialized medical institution must be visited, which is time-consuming; further, the procedure requires technique. In contrast, measuring the occlusal force is simple and requires no special technique. The measuring equipment is portable; therefore, it can be measured at various places in communities. We considered that if a certain relationship between occlusal force and FMD is found, occlusal force evaluation could be an indicator for the elderly to understand their general condition. However, only a few studies examined the relationship between occlusal force and FMD.
This study aimed to investigate the relationship between occlusal force and FDM and to evaluate advanced glycation end products (AGEs) as an indicator of aging and grip strength as an indicator of muscle strength. Furthermore, it was examined whether occlusal force could be a new indicator for preventative medical services in communities.

| Participants
In this study, 38 elderly women (76.7 ± 5.7 years) were analyzed. The participants were aged >65 years during the investigation, living in their own homes, walking independently, and participating in their community salon programs or preventative care more than once a week. The exclusion criteria were those with severe dementia, higher functional disabilities, severe diabetes and heart diseases, severe medical illnesses, functional or organic oral cavity problems, and those who cannot occlude their upper and lower molars (sections), not limited to their teeth.
First, community salons in each area were visited to explain the outline of our research and to request participation in this study.
Following this, a dental hygienist conducted a survey wherein the numbers of teeth of individuals who agreed to participate in the study were determined (primary survey). Furthermore, participants who agreed to participate in a secondary survey underwent a second survey, and parameters other than the number of teeth were measured at the Yamagata Prefectural University of Health Sciences.
After the primary survey of 71 respondents, a small number of male subjects were excluded. Furthermore, the secondary survey excluded 27 subjects because they refused to participate, could not be contacted, and so forth; therefore, the total number of subjects in this study was 38. interfaces between the lumen and vessel wall was obtained, both tracking gates were placed on the intima, the artery diameter was automatically tracked, and the waveform of diameter changes over a cardiac cycle was displayed in real time using the FMD mode of the tracking system. After measuring the blood pressure, the blood pressure cuff was inflated to 50 mmHg above the systolic pressure for 5 min and released. Blood vessel diameter changes were measured for 2 min after the 5 min inflation. The baseline diameter was defined by measuring the minimum blood vessel diameter for 20 s after releasing the blood pressure cuff. FMD was automatically calculated as a percentage change in peak vessel diameter from the baseline value. The reference value was 7% or more.

| Endothelial function
Endothelial dysfunction was suspected in less than 4% (Maruhashi et al., 2019). Figure 1a-c shows the measuring tool and subjects' position.

| Occlusal force
The occlusal force was measured using an occlusal force meter (GM10; Nagano Keiki, Japan) (Figure 1a,b). Measurements were taken twice on the right and left sides and the larger value was considered the final value. The subjects were instructed to bite as hard as possible to take measurements during contraction (Kato et al., 2020).

| AGEs
An increasing level of AGEs was thought to affect aging. Thus, as indicators of aging, these were measured using an AGE Reader (AGE Reader SU 4; Dignoptics, Netherlands) (Haus et al., 2007;Semba et al., 2010). The subjects were seated with their forearm on the AGE Reader in a prone position (Meerwaldt et al., 2004).
Three measurements were on the same side of the forearm and the average value was considered the final value.

| Grip strength
Grip strength was measured using a Jamar hand dynamometer (SH-5001; SAKAI Med, Japan). The subjects were seated with their elbow joint flexed at 90°and both their feet shoulder-width apart.
Measurements of the dominant hand were taken twice and the largest value was considered in the prone position (Meerwaldt et al., 2004) as the final value.

| Statistical analysis
The normality of the data was confirmed using the Shapiro-Wilk test. Correlations between parameters were assessed by bivariate simple correlation analysis. For age, occlusal force, grip strength, FMD, and AGEs, spearman's rank correlation coefficient was used for analysis. Multiple regression analysis was performed on the degree of FMD as a dependent variable and occlusal force, grip strength, AGEs, and age as independent variables. IBM SPSS version 24 (IBM Japan, Tokyo, Japan) was used for all analyses, and p < .05 was considered statistically significant.

| RESULTS
The total number of subjects in this study was 38 and their characteristics are shown in Table 1. The mean age of the subjects was 76.5 ± 5.7. Table 2 shows their grip strength, occlusal force, AGEs, and FMD. Table 3 shows the correlation coefficient for age, occlusal force, grip strength, FMD, and AGEs. There was a significant correlation between occlusal force and grip strength (r = .54 and p < .01). The degree of FMD significantly was associated with occlusal force (r = .60 and p < .01) and grip strength (r = .35 and p < .05) or

| DISCUSSION
In this study, the relationships among oral function, FMD, and AGEs were investigated. We think that occlusal forces, FMD, and AGEs can be useful in understanding the general condition of the elderly in preventative care. This is the first study to investigate the relationship between occlusal force and FMD. Many previous studies have focused on occlusal force and grip strength (Hatta et al., 2019;Umeki et al., 2018;Yamaguchi et al., 2018). In this study, a relationship was found between occlusal force and grip strength, which was consistent with the results reported in previous studies.

AGEs were measured as indicators of aging. Previous studies
showed that AGEs accumulate with age (Haus et al., 2007;Semba et al., 2010). However, in the present study, no specific relationship between AGEs and age was found. However, their detailed life background was not examined. In the future, we may be able to prove the relationship by conducting a survey that includes the subjects' life backgrounds.
The results of this study indicate a relationship between occlusal force and FDM. To the best of our knowledge, only a few studies investigated the relationship between occlusal force and endothelial function. This is a novel finding. From a functional and structural point of view, endothelial dysfunction may result in a reduced blood flow through the microcirculation, which may lead to muscle fiber atrophy. A previous study reported a strong correlation between blood flow volume changes and muscle protein synthesis changes (Rasmussen et al., 2006). Furthermore, endothelial dysfunction also leads to a decreased secretion of vascular endothelial growth factor (VEGF), facilitating functional muscle ischemia; moreover, a decreased secretion of VEGF in association with endothelial dysfunction may lead to a negative muscle protein balance (Zempo et al., 2017).
Residents need to understand their health condition and live consciously in preventative care. Therefore, a simple indicator is necessary. Both occlusal force and FMD are useful for understanding the general condition of the elderly. However, to measure the FMD, a specialized medical institution must be visited, which is time- male elderly people was also not ascertained. In the future, we would like to collect and analyze data from multiple populations. Second, the possible effects of medications and existing diseases on the outcomes could not be ruled out. Third, this study was designed as a cross-sectional study and could not evaluate the causal relationship between the reduced occlusal forces and decreased endothelial function. Further research is needed to overcome these limitations.

| CONCLUSION
In conclusion, in this study, a relationship was found between occlusal force and endothelial function in community-dwelling elderly women. Measuring the occlusal force is easier than measuring FMD.
Therefore, the occlusal force can be an important indicator of the general condition and high-risk diseases that shorten the healthy life expectancy of the elderly.

AUTHOR CONTRIBUTIONS
Kanna Kato: study concept and design, acquisition of subjects and/or data, analysis and interpretation of data, and preparation of the manuscript. Matsuda Naoko: acquisition of subjects and/or data, analysis and interpretation of data, and preparation of the manuscript. Miki Takahata: acquisition of subjects and/or data, analysis and interpretation of data, and preparation of the manuscript. Chika Koseki: acquisition of subjects and/or data and preparation of the manuscript. Michiyasu Yamaki: study concept and design and preparation of the manuscript. Toshiaki Sato: study concept and design, acquisition of subjects and/or data, and analysis.

CONFLICT OF INTEREST
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.